1. Field of the Invention
This invention relates to a new differential pressure transmitter that comprises a linear air velocity transmitter and to a pneumatically operated square root extracting device for such a transmitter or the like as well as to methods of making such a transmitter and/or such a square root extracting device.
2. Prior Art Statement
It is known to provide a differential pressure transmitter comprising means for producing an output pneumatic signal from a pneumatic source in relation to the air velocity pressure of air flowing in a passage, means for sensing the difference between the total pressure and the static pressure of the air flowing in the passage, and means for extracting the square root of the air velocity pressure of the air from the pneumatic output signal as the pneumatic output signal is being produced so that the pneumatic output signal is substantially linear with respect to the air velocity of the air flow in the passage whereby the transmitter comprises a linear air velocity transmitter, the means for extracting the square root comprising a cam having a cam face that defines at least part of the involute of a circle, a roller having a surface that defines a substantially circular transverse cross-sectional configuration, the roller carrying the cam so that the cam rotates as the roller rolls on the surface thereof, a flat surface engaged by the surface of the roller so that the roller can roll on the flat surface, a movable wall carried by the transmitter and defining an output signal chamber therewith whereby the position of the wall is determined by the value of the pressure in the output signal chamber, rod means operatively interconnecting the wall to the roller to roll the roller on the flat surface as the value of the pressure in the output chamber changes, and a cable, the means for producing the output signal comprising a bleed nozzle carried by the transmitter and a flapper lever pivotally carried by the transmitter for controlling the bleed nozzle, the means for sensing the difference between the total pressure and the static pressure comprising a housing having a pair of chambers separated from each other by a flexible diaphragm whereby one of the chambers is for receiving the total pressure therein and the other of the chambers is for receiving the static pressure therein, the flexible diaphragm having a post that is operatively interconnected to the flapper lever to transmit movement of the diaphragm to the flapper lever which will produce the output pneumatic signal with the nozzle, the cam face of the cam being operatively interconnected to the flapper lever by the cable, the cable having opposed ends one of which is operatively interconnected to the flapper lever and the other of which is secured to the cam face in such a manner that the cable is wound onto the cam face as the roller rolls on the flat surface in one direction and is unwound from the cam face as the roller rolls on the flat surface in the opposite direction to the one direction. For example, see the copending patent application of Clarence M. Asbill, III, Ser. No. 114,789, filed Oct. 30, 1987, now U.S. Pat. No. 4,833,924.
Also see the Kreuter U.S. Pat. No. 4,384,492 which discloses another differential pressure transmitter.
It is also known to provide a differential pressure transmitter comprising means for producing an output pneumatic signal from a pneumatic source in relation to the air velocity pressure of air flowing in a passage, means for sensing the difference between the total pressure and the static pressure of the air flowing in the passage, and means for extracting the square root of the air velocity pressure of the air from the pneumatic output signal as the pneumatic output signal is being produced so that the pneumatic output signal is substantially linear with respect to the air velocity of the air flow in the passage whereby the transmitter comprises a linear air velocity transmitter, the means for extracting the square root comprising a cam arrangement, a movable wall carried by the transmitter and defining an output signal chamber therewith whereby the position of the wall is determined by the value of the pressure in the output signal chamber, the wall being operatively interconnected to the cam arrangement to operate the cam arrangement as the value of the pressure in the output chamber changes, the means for producing the output pneumatic signal comprising a bleed nozzle carried by the transmitter and a flapper lever pivotally carried by the transmitter for controlling the bleed nozzle, the means for sensing the difference between the total pressure and the static pressure comprising a housing having a pair of chambers separated from each other by a flexible diaphragm whereby one of the chambers is for receiving the total pressure therein and the other of the chambers is for receiving the static pressure therein, the flexible diaphragm having a post that is operatively interconnected to the flapper lever to transmit movement of the diaphragm to the flapper lever which will produce the output pneumatic signal with the nozzle, the cam arrangement being operatively interconnected to the flapper lever, the housing having two like end diaphragms disposed on opposite sides of the flexible diaphragm and provided with outer peripheries respectively secured to the housing and inner peripheries respectively secured to two parts of the post whereby the end diaphragms respectively cooperate with the flexible diaphragm to define the pair of chambers therebetween. For example, see the aforementioned copending patent application of Clarence M. Asbill, III, Ser. No. 114,789, filed Oct. 30, 1987.
Also see the aforementioned Kreuter U.S. Pat. No. 4,384,492 for another differential pressure transmitter.